Two-dimensional Kinematics of SLACS Lenses. 1. Phase-space Analysis of the Early-Type Galaxy SDSS J2321-097 at z=0.1

Nov, 2007
17 pages
Published in:
  • Mon.Not.Roy.Astron.Soc. 384 (2008) 987
e-Print:

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Abstract: (arXiv)
We present the first results of a combined VLT VIMOS-IFU and HST-ACS study of the early-type lens galaxy SDSS J2321-097 at z=0.0819, extending kinematic studies to a look-back time of 1 Gyr. This system, discovered in the Sloan Lens ACS Survey (SLACS), has been observed as part of a VLT Large Programme with the goal of obtaining two-dimensional stellar kinematics of 17 early-type galaxies to z~0.35 and Keck spectroscopy of an additional dozen lens systems. Bayesian modelling of both the surface brightness distribution of the lensed source and the two-dimensional measurements of velocity and velocity dispersion has allowed us to dissect this galaxy in three dimensions and break the classical mass--anisotropy, mass-sheet and inclination--oblateness degeneracies. Our main results are that the galaxy (i) has a total density profile well described by a single power-law \rho propto r^{-\gamma'} with \gamma' = 2.06^{+0.03}_{-0.06}/ (ii) is a very slow rotator (specific stellar angular momentum parameter \lambda_R = 0.075), well approximated under the assumption of axisymmetry by a superposition of orbits which conserve the two classical integrals of motion, E and L_z/ (iii) shows only mild anisotropy (\delta ~ 0.15)/ and (iv) has a dark-matter contribution of ~30 per cent inside the effective radius. Our first results from this large combined imaging and spectroscopic effort with the VLT, Keck and HST show that the structure of massive early-type galaxies beyond the local Universe can now be studied in great detail using the combination of stellar kinematics and gravitational lensing. Extending these studies to look-back times where evolutionary effects become measurable holds great promise for the understanding of formation and evolution of early-type galaxies.
  • GALAXIES ELLIPTICAL
  • GALAXIES LENTICULAR
  • GALAXIES CD
  • GALAXIES STRUCTURE
  • GALAXIES KINEMATICS
  • GALAXIES DYNAMICS
  • TECHNIQUES SPECTROSCOPIC
  • GRAVITATIONAL LENSING